a) Field of the Invention
This invention relates to a pressure control valve arrangement in a hydraulically-actuated differential or torque coupling device for use with a vehicle drive train, for example, a speed sensitive limited slip differential; and more particularly is directed to a multi-control valve assembly for a hydraulically actuated clutch pack in a torque coupling device.
b) Background of Related Art
Limited slip differentials and torque coupling devices are well known in the art. In such devices, a hydraulically actuated friction clutch pack is actuated to retard relative rotation of at least one of the rotating component, e.g., at least on side gears relative to the differential case. Normally, hydraulic pressure is directly increased in response to an increase in rotational speed differential of the axle components. One common way to provide the hydraulic pressure is to include an internal pump, or gerotor pump, within a differential case. As hydraulic pressure increases as a result of the increased speed of the pump (increased speed differential), there is a need to provide a pressure relief valve to provide relief from pressure build up in the limited slip device. In other words, once the hydraulic pressure reaches a predetermined level, the pressure relief valve relieves that pressure.
One such pressure relief valve of the related art is shown in FIG. 7. A ball is simply provided in a ball seat on the external surface of the differential case. The ball seat is in communication with hydraulic fluid of the limiting device. The ball is retained in the seat by a leaf spring secured to the outer surface of the differential case. As hydraulic pressure in the limiting device increased, the ball is forced against the leaf spring. If sufficient pressure exists, the leaf spring opens and fluid is allowed to flow out of the differential case. Otherwise, the valve remains closed.
It is also known to provide a hydraulic valve assembly including a bleed passage to control how the hydraulic pressure in the hydraulic system rises with increased flow. However, the prior art fails to adequately provide variable pressure control, linear and non-linear as well as thermo-sensitive compensation for changes in fluid viscosity with temperature.
The need therefore exists for an improved differential control valve that is simple in design, easy to assembly and opens and closes in a predictable and consistent manner, while integrating two distinct hydraulic flow and pressure mechanisms into a single assembly.
The present invention provides an improved pressure control valve for use in a limited slip differential or torque coupling device. A pressure control valve assembly is disposed in the hydraulic flow path of a differential assembly and is connected to a passageway leading to a limited slip device within the differential case to establish fluid communication there between.
In the preferred embodiment, the invention includes a machined or formed blind hole, a groove which partially intersects the blind hole, a ball member seated in the blind hole, and a spring resiliently acting on the ball to apply a force biasing the ball into the blind hole. At the intersection of the blind hole and groove, an area, which is not sealed by the ball, is formed that provides a controlled leakage path for the hydraulic fluid. As the hydraulic fluid flow increases, the hydraulic pressure of the fluid on the pressure side increases which increases the force on the ball acting against the spring. As the pressure increases further, the resultant forces on the ball deflect the spring to increase the bleed area and increase the fluid bled proportionally to the fluid pressure. Therefore, a pressure control mechanism is provided.
The pressure control valve controls the pressure flow in a manner that can be controlled by changing the dimensions of the hole, groove and ball. Hydraulic flow leakage and pressure control can vary with the force of the spring.
In a modified embodiment of this invention, a temperature sensitive spring is used (e.g., as a bi-metallic member) to allow the force on the ball to vary with temperature to either decrease upper pressure values at higher temperature or increase upper pressure with increase in temperature, or to provide compensation for change in fluid viscosity with temperature.
The objects, features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings.